Abstract 4662: “Number Needed to Replace” (NNR): A Novel Algorithm to Decide Whether to Replace a Device Listed on an Advisory Letter
In recent years, manufacturers have issued an increased number of “Advisory” letters concerning potential device/lead malfunctions. As device replacement imposes certain risks and some patients are far less dependent than others on proper device functioning, deciding if and when to replace an “advisory” device requires careful consideration. We have developed an algorithm providing the “number needed to replace” (NNR) to save one life. This equation is based on four parameters, which determine the risk/benefit ratio for replacing a device: a) difference in failure rate between the currently implanted device and its replacement; b) risk associated with the replacement intervention; c) the patient’s dependence on device therapy (his/her “arrhythmia risk”); d) remaining device battery life. (“Harm” represents situation where replacement is associated with greater risk for mortality than not replacing.) Assuming the 0.4% mortality for replacement procedures (Canadian multicenter study, Gould and Krahn, JAMA 2006), the algorithm yields the NNR values shown in the Figure⇓ below. Pacemaker-dependent patients (annual arrhythmic risk 100%) implanted with devices with ≥ 0.5% failure rate have NNR < 250, hence replacement could be reasonable. Conversely, replacement in patients with ≤2.5%/year arrhythmic risk may be harmful. Replacement of devices with ≤ 0.1% failure rate will result in very high NNR (> 250) or even harm. The NNR calculation helps in the device replacement decision by quantifying the associated risk/benefit ratio. The risk and complications associated with replacing leads would generally argue against doing so.